U.S. patent number 5,390,274 [Application Number 07/908,603] was granted by the patent office on 1995-02-14 for distributed graded index type optical transmission plastic article and method of manufacturing same.
This patent grant is currently assigned to Mitsubishi Rayon Company Ltd.. Invention is credited to Teruta Ishimaru, Yoshihiko Mishina, Ryuji Murata, Masaaki Oda, Nobuhiko Toyoda, Yoshihiro Uozu.
United States Patent |
5,390,274 |
Toyoda , et al. |
February 14, 1995 |
**Please see images for:
( Certificate of Correction ) ** |
Distributed graded index type optical transmission plastic article
and method of manufacturing same
Abstract
A distributed refractive index type optical transmission plastic
article has a circular cross section of a radius r.sub.0 which is
in a range of 0.4 to 0.6 mm. A refractive index distribution of the
optical transmission article substantially approximates a
predetermined ideal refractive index distribution curve at least in
a range of 0.25r.sub.0 to 0.70r.sub.0 extending from a center axis
toward a peripheral surface of the article. A refractive index
n.sub.0 at a central part of the article is in a range of 1.4 to
1.6. The article has a refractive index distribution constant of
larger than 0.15 mm.sup.-1 and smaller than 0.3 mm.sup.-1, and a
modulation transfer function of at least 55%. This optical
transmission article is made from uncured liquid substances each
having a viscosity of between 10.sup.3 and 10.sup.8 poises. N
(N.gtoreq.2) uncured liquid substances having refractive indexes n
of n.sub.1 >n.sub.2 >n.sub.3 . . . n.sub.N when cured are
arranged in such a way that the refractive indexes n are
successively reduced from a central portion toward a peripheral
portion, and concentrically laminated one upon the other to form an
uncured strand fiber. The substances between adjacent layers of the
fiber are mutually diffused. During the diffusion or thereafter,
the uncured strand fiber is cured, thereby completing the
production of the optical transmission article.
Inventors: |
Toyoda; Nobuhiko (Otake,
JP), Mishina; Yoshihiko (Otake, JP),
Murata; Ryuji (Otake, JP), Uozu; Yoshihiro
(Otake, JP), Oda; Masaaki (Otake, JP),
Ishimaru; Teruta (Otake, JP) |
Assignee: |
Mitsubishi Rayon Company Ltd.
(Tokyo, JP)
|
Family
ID: |
13958872 |
Appl.
No.: |
07/908,603 |
Filed: |
July 30, 1992 |
PCT
Filed: |
September 29, 1989 |
PCT No.: |
PCT/JP89/00991 |
371
Date: |
May 24, 1991 |
102(e)
Date: |
May 24, 1991 |
PCT
Pub. No.: |
WO91/05275 |
PCT
Pub. Date: |
April 18, 1991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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689880 |
May 24, 1991 |
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Current U.S.
Class: |
385/124; 359/900;
385/120; 359/654 |
Current CPC
Class: |
G02B
6/02038 (20130101); G02B 6/06 (20130101); Y10S
359/90 (20130101) |
Current International
Class: |
G02B
6/028 (20060101); G02B 6/06 (20060101); G02B
6/02 (20060101); G02B 006/18 () |
Field of
Search: |
;385/115,116,120,121,123,124 ;359/652,653,654,900 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0208159 |
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Jan 1987 |
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EP |
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0242636 |
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Oct 1987 |
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EP |
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62-209402 |
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Sep 1987 |
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JP |
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62-215204 |
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Sep 1987 |
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JP |
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Other References
Lama, William; Applied Optics, "Optical Properties of GRIN Fiber
Lens Arrays: Dependence of Fiber Length", vol. 21, No. 15, pp.
2739-2746, Aug. 1982..
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Primary Examiner: Lee; John D.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier,
& Neustadt
Parent Case Text
This application is a continuation of application Ser. No.
07/689,880, filed on May 24, 1991, now abandoned.
Claims
We claim:
1. A distributed refractive index type optical transmission plastic
article having a circular cross section of a radius r.sub.0 and a
refractive index distribution which substantially approximates a
refractive index distribution curve defined by the following
equation (1) at least in a range of 0.25r.sub.0 to 0.70r.sub.0
extending from a center axis toward a peripheral surface of the
optical transmission article:
where n.sub.0 is a refractive index at the center axis of the
optical transmission article;
n(r) is a refractive index at a position of radius r away from the
center axis of the optical transmission article;
g is a refractive index distribution constant (mm.sup.-1) of the
optical transmission article;
r is a distance (mm) from the center axis toward the peripheral
surface of the optical transmission article; and
1.4.ltoreq.n.sub.0 .ltoreq.1.6
0.4.ltoreq.r.sub.0 (mm).ltoreq.0.6
0.15.ltoreq.g (mm.sup.-1)<0.3
wherein when a grid image of 4 line-pairs/mm is formed through the
optical transmission article on a CCD line sensor and a maximum
value i.sub.max and a minimum value i.sub.min of light quantities
of the image are measured, a modulation transfer function (MTF)
calculated according to the following equation (2):
is at least 55%.
2. A distributed refractive index type optical transmission plastic
article as set forth in claim 1, wherein the refractive index
distribution of the optical transmission article substantially
approximates the refractive index distribution curve defined by the
equation (1) at least in a range of 0.20r.sub.0 to 0.75r.sub.0
extending from the center axis toward the peripheral surface of the
optical transmission article.
3. A method of manufacturing a distributed refractive index type
optical transmission plastic article comprising the steps of
preparing N (N.gtoreq.2) uncured liquid substances having a
viscosity between 10.sup.3 and 10.sup.8 poises each and refractive
indexes n of n.sub.1 >n.sub.2 >n.sub.3 . . . n.sub.N when
cured, concentrically laminating the substances in such a way that
the refractive indexes are successively reduced from the center
toward the periphery of the laminated substances to form an uncured
strand fiber, mutually diffusing the substances between adjacent
layers in such a way that the refractive indexes are continuously
distributed between the layers, and thereafter, curing the uncured
strand fiber.
4. An optical transmission article array comprising an assembly of
a plurality of distributed refractive index type plastic optical
transmission articles arranged in a single line or a plurality of
lines, said distributed refractive index type optical transmission
plastic articles each having a circular cross section of a radius
r.sub.0 and a refractive index distribution which substantially
approximates a refractive index distribution curve defined by the
following equation (1) at least in a range of 0.25r.sub.0 to
0.70r.sub.0 extending from a center axis toward a peripheral
surface of the optical transmission article:
where n.sub.0 is a refractive index at the center axis of the
optical transmission article;
n(r) is a refractive index at a position of radius r away from the
center axis of the optical transmission article;
g is a refractive index distribution constant (mm.sup.-1) of the
optical transmission article;
r is a distance (mm) from the center axis toward the peripheral
face of the optical transmission article; and
1.4.ltoreq.n.sub.0 .ltoreq.1.6
0.4.ltoreq.r.sub.0 (mm).ltoreq.0.6
0.15.ltoreq.g (mm.sup.-1)<0.3
wherein when a grid image of 4 line-pairs/mm is formed through the
optical transmission article on a CCD line sensor and a maximum
value i.sub.max and a minimum value i.sub.min of light quantities
of the image are measured, a modulation transfer function (MTF)
calculated according to the following equation (2):
is at least 55%.
Description
TECHNICAL FIELD
The present invention relates to an optical transmission article
and a method of manufacturing same, which is useful for optical
transmission lines such as near parabolic optical fibers, rod-like
convergent lenses, and photosensors, as well as for an image
transmitting array employed in a copying machine using a white
light source.
BACKGROUND ART
Optical transmission articles each with refractive indexes
gradually distributed from the center toward the periphery on a
cross-section thereof are disclosed in Japanese Examined Patent
Publication No. 47-816, Japanese Examined Patent Publication No.
47-28059, and European Patent Publication No. 0208159.
The distributed refractive index type optical transmission article
disclosed in Japanese Examined Patent Publication No. 47-816 is
made of glass and fabricated by an ion exchange method. This
method, however, has a poor productivity and cannot produce
articles having an identical shape (an identical length, in
particular) and an identical performance. Even with an identical
performance, the fabricated distributed refractive index type
optical transmission articles have different lengths, and thus
problems arise with the handling thereof.
The distributed refractive index type optical transmission plastic
article disclosed in Japanese Examined Patent Publication No.
47-28059 is made by mixing two or more transparent polymers having
different refractive indexes and different solubilities with
respect to a particular solvent. The mixed polymers are shaped into
a rod or a fiber, and immersed in the solvent to extract a part of
the polymers from the surface thereof, thereby changing a mixing
ratio of the polymers from the surface toward the center thereof.
Since the optical transmission article of this method is made of a
mixture of two or more polymers having different refractive
indexes, fluctuations in the refractive indexes of the article
occur, deteriorating the transparency and causing light scattering,
and therefore, the article cannot serve as the distributed
refractive index type optical transmission article. Accordingly,
little improvement can be expected in the application and
development of this method.
European Patent Publication No. 0208159 describes a method in which
(A) at least one kind of thermoplastic polymer and (B) a monomer
which is compatible with the polymer (A) when polymerized and forms
a polymer having a refractive index different from that of the
polymer (A), are mixed and formed into a rod-like shape. From the
surface of the shaped body, the monomer (B) is volatilized to
continuously distribute the monomer (B) from the surface toward the
interior of the formed material, and thereafter, the
non-polymerized monomer in the shaped body is polymerized to form a
distributed refractive index type optical transmission plastic
article.
An ideal refractive index distribution curve of the distributed
refractive index type optical transmission article is expressed as
follows:
This curve is considered to be the same as a curve "a" of FIG.
2.
According to studies and measurements made by the inventor, using
an Interfaco interference microscope under conditions to be
explained later, however, the distributed refractive index type
optical transmission article fabricated according to the
above-mentioned method provides a refractive index distribution
curve "b" of FIG. 2. In a range of 0.5r.sub.0 to 0.75r.sub.0 of
radial distances from the center (i.e., in a range of c to d in the
figure, with e being an outermost part), the curve b is relatively
close to the ideal curve expressed by the equation (1). At the
outer and inner sides of the above range, however, the refractive
index distribution is greatly deviated from the ideal curve.
When a grid pattern is observed through these optical transmission
articles, if the optical transmission article has a refractive
index pattern which almost correctly follows the quadratic curve
defined by the equation (1), the article will provide a normal grid
image as shown in FIG. 3(a). If, however, the refractive index
distribution of the optical transmission article deviates from the
ideal refractive index distribution, as indicated by (b) of FIG. 2,
the article will provide a distorted grid image as shown in FIGS.
3(b) and 3(c), since the article can not transmit a correct image.
In this case, a moderation transfer factor (MTF) indicating the
resolution of the article is very low, i.e., less than 30%, which
is not acceptable for use as an optical transmission article of a
copying machine.
Accordingly, the conventional distributed refractive index type
optical transmission article with the refractive index distribution
as shown by (b) of FIG. 2 must be cut or eluted by a solvent
process to remove a portion outer than the position (d) of FIG. 2,
thereby providing the optical transmission article with an optical
path having a relatively ideal refractive index distribution. It
is, however, difficult to provide an optical transmission article
with a high resolution, and thus the productivity thereof is very
low, and it is very difficult to constantly produce products having
a uniform quality.
DISCLOSURE OF THE INVENTION
An object of the invention is to provide a distributed refractive
index type optical transmission plastic article which can be
applied to a copying machine employing a white light source.
Compared with the conventional optical transmission articles, the
optical transmission article of the invention has a higher
resolution, is brighter, and obtains a remarkably improved
productivity.
The invention provides a distributed refractive index type optical
transmission plastic article having a circular cross section of a
radius r.sub.0 and a refractive index distribution which
substantially approximates a refractive index distribution curve
defined by the following equation (1), at least in a range of
0.25r.sub.0 to 0.70r.sub.0 extending from a center axis toward a
peripheral surface of the optical transmission article:
where n.sub.0 is a refractive index at the center axis of the
optical transmission article;
n(r) is a refractive index at a position of a radius r away from
the center axis of the optical transmission article;
g is a refractive index distribution constant (mm.sup.-1) of the
optical transmission article; and
r is a distance (mm) from the center axis toward the peripheral
surface of the optical transmission article, wherein,
1.4.ltoreq.n.sub.0 .ltoreq.1.6
0.4.ltoreq.r.sub.0 (mm).ltoreq.0.6
0.15.ltoreq.g (mm.sup.-1)<0.3
said distributed refractive index type optical transmission plastic
article having a modulation transfer function (hereinafter referred
to as the MTF) of not less than 55%, calculated according to the
following equation (2):
when a grid image of 4 line-pairs/mm is formed through the optical
transmission article on a CCD line sensor and a maximum value
i.sub.max and a minimum value i.sub.min of light quantities of the
image are measured.
The invention also provides a method of manufacturing the
distributed refractive index type optical transmission plastic
article. This method employs N (N.gtoreq.2) uncured liquid
substances each having a viscosity of between 10.sup.3 and 10.sup.8
poises and refractive indexes n of n.sub.1 >n.sub.2 >n.sub.3
. . . n.sub.N when cured, concentrically laminates the substances
in such a way that the refractive indexes are successively reduced
from the center toward the periphery of the laminated substances to
form an uncured strand fiber, mutually diffuses the substances
between adjacent layers in such a way that the refractive indexes
are continuously distributed between the layers, and at the same
time or thereafter, cures the uncured strand fiber.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a refractive index distribution curve of an example of
distributed refractive index type optical transmission articles of
the invention;
FIG. 2 shows a refractive index distribution curve of a distributed
refractive index type optical transmission plastic article formed
according to a prior art method;
FIGS. 3a-3c are views of examples of grid images obtained by these
optical transmission articles;
FIG. 4 is a schematic view of an apparatus for measuring the
resolution of an optical transmission article;
FIG. 5 is a graph showing the light quantity levels of a grid image
measured with a CCD sensor;
FIG. 6 is a schematic view of an apparatus preferably used for
forming the distributed refractive index type optical transmission
plastic article of the invention;
FIG. 7 is a schematic view of a lens capacity measuring apparatus;
and
FIG. 8 shows a refractive index distribution curve of an example of
distributed refractive index type optical transmission plastic
optical articles of the invention.
BEST MODE OF CARRYING OUT THE INVENTION
As indicated by (b) of FIG. 1, a refractive index distribution
curve of the optical transmission article of the invention must
substantially approximate the ideal refractive index distribution
curve ((a) of FIG. 1) expressed with the equation (1), at least in
a range of 0.25r.sub.0 to 0.70r.sub.0 , preferably 0.20r.sub.0 to
0.75r.sub.0 , from a center axis. If a distributed refractive index
type optical transmission plastic article has a refractive index
distribution curve which does not approximate the refractive index
distribution curve (a) of FIG. 1 expressed with the equation (1),
in a range of 0.25r.sub.0 to 0.75r.sub.0 from a center axis, the
optical transmission article cannot correctly transfer images or
satisfy the requirements for an optical transmission article
applied to a copying machine, and therefore, can not be applied for
such a purpose.
The distributed refractive index type optical transmission plastic
article of the invention must have a value n.sub.0 of
1.4.ltoreq.n.sub.0 .ltoreq.1.6. If the value exceeds 1.6, the
optical transmission plastic article is difficult to produce, and
if the value n.sub.0 is smaller than 1.4, a difference of
refractive indexes at the center axis and at the periphery of the
article cannot be enlarged, to thus realize an optical transmission
article having an excellent resolution and image transmitting
characteristics.
A value g is defined by the following equation (3): ##EQU1## which
defines a lens length and an image forming length. When the value g
is greater than 0.3 mm.sup.-1, the optical transmission article may
have a chromatic aberration, and therefore, may not be appropriate
for an optical transmission article used with a white light source.
When the value g is smaller than 0.15 mm.sup.-1, the optical
transmission article may have a long image forming length and be
difficult to handle.
When the distributed diffraction index type optical transmission
plastic article of the invention is used for a copying machine,
etc., a plurality of such articles, instead of a single article,
are usually arranged in a single row or a plurality of rows in a
zigzag manner, to form an array of the optical transmission
materials in which images provided by the articles partly overlap
each other to form an image. The visibility of the overlapped
images depends on the degree of overlapping, which is influenced by
the diameter of each optical transmission article. To obtain a
clear image, the radius r.sub.0 must be in a range of 0.4 to 0.6
mm. If the article is thinner than this, the article may have an
insufficient brightness and difficult to produce with a uniform
refractive index distribution. If the article is thicker than the
above range, the images provided by the array of the optical
transmission articles may unevenly overlap each other, and thus
will not transmit clear images.
The MTF, which indicates resolution of the distributed refractive
index optical transmission plastic article of the invention, can be
determined as follows. Namely, as shown in FIG. 4, a light source
42, a filter 43, a diffusion plate 44, a grid 45, and an array 47
composed of a plurality of distributed refractive index type
optical transmission articles 41 form a resolution measuring
apparatus. A grid image having a spatial frequency of 4
(line-pairs/mm) is passed through the optical transmission articles
41 to form an image on a CCD line sensor 46. The formed grid image
is read, and a maximum value (i.sub.max) and a minimum value
(i.sub.min) of light quantities of the image are measured as shown
in FIG. 5. According to the measured i.sub.max and i.sub.min, the
MTF is calculated from the following equation (2):
where the grid constant is the number of lines per millimeter
(line-pairs/mm), in which each line comprises a pair of white and
black lines as shown on the grid 45 of FIG. 4.
The MTF of the distributed refractive index type optical
transmission plastic article of the invention must be not less than
55%. If the MTF is smaller than 55%, the optical transmission
article provides a low resolution and cannot form a clear image
when applied to a copying machine such as a facsimile.
The distributed refractive index type optical transmission plastic
article of the invention may be fabricated in the following
manner:
N (N.gtoreq.2) uncured liquid substances each having a viscosity of
between 10.sup.3 and 10.sup.8 poises in an uncured state and
refractive indexes n of n.sub.1 >n.sub.2 >n.sub.3 . . .
n.sub.N in a cured state are prepared, and these uncured liquid
substances are concentrically laminated, one upon the other, in
such a way that the refractive indexes are successively reduced
from the center toward the periphery of the laminated substances,
thereby forming an uncured strand fiber. The substances of the
strand fiber are then mutually diffused between adjacent layers to
provide a continuous refractive index distribution between the
layers, during which or thereafter the uncured strand fiber is
cured.
If N.gtoreq.2 is established in the distributed refractive index
type optical transmission article having the value g of
0.3>g.gtoreq.0.15, a required difference n.sub.1 -n.sub.N may be
set between a center layer and an outermost layer of the optical
transmission material, and accordingly, it will become easy to
fabricate the optical transmission article of the invention having
a refractive index distribution which approximates the curve of the
equation (1), in a range of 0.25r.sub.0 to 0.75r.sub.0 from the
center of the article. Accordingly, N must be 2 or greater than 2,
preferably 2 to 7, and more preferably 3 to 5.
When carrying out the invention, each of the uncured liquid
substances must have a viscosity of between 10.sup.3 and 10.sup.8
poises and be curable. If the viscosity is smaller than 10.sup.3
poises, the strand will be easily broken and it will be difficult
to form a strand-like shape. If the viscosity is greater than
10.sup.8 poises, the substance will have a poor shaping
processability which will lead to a deterioration of the
concentricity or the forming of irregular diameters.
The liquid substances to be employed when carrying out the
invention may be radical polymerizable vinyl monomers, or
compositions comprising the monomers and polymers that are soluble
with the monomers.
The radical polymerizable vinyl monomers are, for example, methyl
methacrylate (n=1.49), styrene (n=1.59), chlorostyrene (n=1.61),
vinyl acetate (n=1.47), fluorized alkyl(meta)acrylate (n=1.37 to
1.44) such as 2,2,3,3-tetrafluoropropyl(meta)acrylate,
2,2,3,3,4,4,5,5-octafluoropropyl(meta)acrylate,
2,2,3,4,4,4-hexafluoropropyl(meta)acrylate, and
2,2,2-trifluoroethyl(meta)acrylate, and (meta)acrylates having a
refractive index between 1.43 and 1.62 such as ethyl(meta)acrylate,
phenyl(meta)acrylate, benzyl(meta)acrylate,
hydroxylalkyl(meta)acrylate, alkyleneglycoldi(meta)acrylate,
trimethylolpropane-di or -tri(meta)acrylate, pentaerythritol-di,
-tri, or -tetra(meta)acrylate, diglycerintetra(meta)acrylate,
dipentaerythritolhexa(meta)acrylate, as well as
diethyleneglycolbisallylcarbonate, fluorized
alkyleneglycolpoly(meta)acrylate, etc.
In order to adjust the viscosities of these cured liquid substances
and make the distribution of the refractive index of an obtained
strand fiber from the center toward the outside of the strand
fiber, the uncured liquid substances are preferably composed of
vinyl-based monomers and soluble polymers. The polymers able to be
used must have a good compatibility with polymers produced from the
radical polymerizable vinyl monomers. These polymers are, for
example, poly(methyl methacrylate) (n=1.49), poly(methyl
methacrylate)-based copolymers (n=1.47 to 1.50),
poly-4-methylpenten-1 (n=1.46), ethylene/vinyl acetate copolymers
(n=1.46 to 1.50), polycarbonate (n=1.50 to 1.57), poly(vinylidene
fluoride) (n=1.42), vinylidene fluoride/tetrafluoroethylene
copolymers (n=1.42 to 1.46), vinylidene
fluoride/tetrafluoroethylene/hexafluoropropene copolymers (n=1.40
to 1.46), and poly(alkyl fluoride)(meta)acrylate polymers.
To adjust the viscosities, it is preferable to use polymers having
an identical refractive index for respective layers, because an
optical transmission plastic article having refractive indexes
continuously distributed from the center toward the surface of the
material can thus be formed. In particular, poly(methyl
methacrylate) has an excellent transparency and a high refractive
index, and therefore, is preferably used for producing the
distributed refractive index type optical transmission article of
the invention.
To cure the strand fiber formed from the uncured substances, it is
preferable to add a thermosetting catalyst and/or photocatalyst to
the uncured substances. The fiber strand containing the
thermosetting catalyst and/or photocatalyst is heated or irradiated
with light, preferably ultraviolet light.
The thermosetting catalyst may be a peroxide-based catalyst, and
the photopolymerization catalyst may be benzophenone,
benzoinalkylether, 4'-isopropyl-2-hydroxy-2-methyl-propiophenone,
1-hydroxycyclohexylphenylketone, benzylmethylketal,
2,2-diethoxyacetophenone, chlorothioxanthone, thioxanthone-based
compounds, benzophenone-based compounds, 4-dimethylaminobenzoic
ethyl, 4-dimethylaminobenzoic isoamyl, N-methyldiethanolamine,
triethylamine, etc.
The light source used for the photopolymerization may be a carbon
arc lamp, a high-pressure mercury lamp, an ultra-high pressure
mercury lamp, a low-pressure mercury lamp, a chemical lamp, a xenon
lamp, or a laser beam, etc., emitting light having a wavelength of
150 to 600 nm.
To produce the optical transmission article of the invention, a
strand fiber forming apparatus shown in FIG. 6, for example, may be
used. A concentric composite nozzle 61 extrudes an uncured strand
fiber 62, which is passed through a mutual diffusion portion 63 for
mutually diffusing monomers of respective layers of the strand
fiber to impart a refractive index distribution, as well as through
a curing portion 64 for curing the uncured substances. The strand
fiber is then passed between pulling rollers 65, and wound, as a
distributed refractive index type optical transmission plastic
article 66, around a winding portion 67. To remove volatilizing
substances released from the strand fiber 62, from the mutual
diffusion portion 63 and from the curing portion 64, an inert gas
such as a nitrogen gas is introduced from an inert gas introducing
port 68, and discharged from a discharging port 69.
The distributed refractive index type optical transmission article
obtained according to the above method may have a coating layer
with a low refractive index. The coating layer can be formed by
mixing trifluoroalkylacrylate, pentafluoroalkylacrylate,
hexafluoroalkylacrylate, fluoroalkylenediacrylate,
1,1,2,2-tetrahydroheptadecafluorodecylacrylate,
hexanedioldiacrylate, neopentylglycoldiacrylate,
dipentaerythritolhexaacrylate, etc. As and when required, polymers
of fluorized acrylate or methacrylate may be added to adjust the
applicability and refractive indexes. In addition, it is preferable
to add photopolymerization initiators,
The invention will be explained in more detail with reference to
Examples.
The lens capacities and refractive index distributions of the
examples were measured as follows:
I. MEASUREMENT OF LENS CAPACITIES
Evaluation Apparatus
The lens capacities were measured with an evaluation apparatus
shown in FIG. 7.
Preparation of Samples
Each optical transmission article prepared according to the
Examples was cut to a length of about one fourth (.lambda./4) of a
period (.lambda.) of a light beam. The period (.lambda.) was
determined from the wave form of a He-Ne laser beam passing through
the article. The article was then polished with a polisher, to make
both end faces of the sample parallel to each other and orthogonal
to a longitudinal axis, and thus a sample to be evaluated was
obtained.
Measuring Method
As shown in FIG. 7, a sample table (76) was placed on an optical
bench (71), and a sample (78) to be evaluated was placed on the
sample table (76). A diaphragm (74) was adjusted so that light from
a light source (72) passes through a condenser lens (73), the
diaphragm (74), and a glass plate (75) and entirely irradiates an
end face of the sample. Thereafter, the sample (78) and a Polaroid
camera (77) were adjusted so that the light was focused on a film
in a Polaroid (a trademark of the Polaroid company) camera. An
image of a square grid was photographed, and a distortion of the
grid was observed. The glass plate (75) was a chrome-plated
photomasking glass, the chrome film on which was precisely
processed to form a square grid pattern of 0.1 mm.
II. MEASUREMENT OF REFRACTIVE INDEX DISTRIBUTION
An Interfaco interference microscope made by the Carl Zeiss company
was used for this measurement.
EXAMPLE 1
Poly(methyl methacrylate) ([.rho.]=0.34 measured in
methylethylketone (MEK) at 25.degree. C.) of 52 parts by weight,
benzylmethacrylate of 35 parts by weight, methylmethacrylate of 13
parts by weight, 1-hydroxycyclohexylphenylketone of 0.2 parts by
weight, and hydroquinone of 0.1 parts by weight were heated and
mixed at 60.degree. C. to form an uncured substance as an original
liquid for forming a first layer (a central portion). Poly(methyl
methacrylate) ([.rho.]=0.34 measured in MEK at 25.degree. C.) of 50
parts by weight, benzylmethacrylate of 15 parts by weight,
methylmethacrylate of 35 parts by weight,
1-hydroxycyclohexylphenylketone of 0.2 parts by weight, and
hydroquinone of 0.1 parts by weight were heated and mixed at
60.degree. C. to form an uncured substance as an original liquid
for forming a second layer. Poly(methyl methacrylate) ([.rho.]=0.34
measured in MEK at 25.degree. C.) of 50 parts by weight,
methylmethacrylate of 50 parts by weight,
1-hydroxycyclohexylphenylketone of 0.2 parts by weight, and
hydroquinone of 0.1 parts by weight were heated and mixed to form
an uncured substance as an original liquid for forming a third
layer (outer layer portion). The three kinds of the original
liquids were simultaneously extruded from a composite nozzle to
form a concentric strand fiber. During this extrusion, the
viscosity of the first layer components was 4.7.times.10.sup.4
poises, that of the second layer components was 3.7.times.10.sup.4
poises, and that of the third layer components was
2.9.times.10.sup.4 poises. The temperature of the composite nozzle
was 60.degree. C. As shown in FIG. 6, the strand fiber 62 extruded
from the nozzle was passed through the mutual diffusion portion
(63) 45 cm in length, to mutually diffuse the monomers between
layers of the strand fiber. Thereafter, the strand fiber was passed
through the center of a light irradiating portion composed of 12
fluorescent lamps (120 cm long, output 40 W) equidistantly arranged
in a ring shape, at a speed of 40 cm/min, and as a result, the
monomers in the strand fiber were polymerized to form a distributed
refractive index type optical transmission plastic article which
was then drawn by nip rollers.
When forming the strand fiber, a ratio f discharged quantities of
the first, second, and third layers was 7:4:1. The distributed
refractive index type optical transmission article thus produced
had a radius (r.sub.0) of 0.59 mm, distributed refractive indexes
measured by the Interfaco interference microscope of 0.508 at a
central portion and 1.498 at a peripheral portion, and a refractive
index distribution constant (g) of 0.20 mm.sup.-1. As shown in FIG.
8, a refractive index distribution of the article substantially
approximated the equation (1), in a range of 0.15r.sub.0 to
0.75r.sub.0 extending from the center toward the external face of
the article. Both end surfaces of the optical transmission article
were polished to a lens length of 18.4 mm, and an MTF thereof was
measured with a grid of 4 line-pairs/mm; the MTF was 60% at a
conjugate length of 42.4 mm. The obtained grid image was clear with
only a minor distortion.
A plurality of the optical transmission articles were employed to
form an optical transmission article array having a lens length of
18.4 mm as indicated by the numeral 47 in FIG. 4, an MTF thereof
was measured with a grid of 4 line-pairs/mm, and it was found that
the MTF was 52%. At this time, a conjugate length of a rod-like
lens forming the optical transmission article array was 42.4 mm.
This optical transmission article array, an LED light source, and a
light receiving CCD element were assembled into an image scanner,
which provided a high resolution and was able to transmit clear
images.
EXAMPLE 2
The three kinds of original liquids used in the Example 1 and a
fourth layer forming original liquid made of poly(methyl
methacrylate) ([.rho.]=0.34 measured in MEK at 25.degree. C.) of 47
parts by weight, methylmethacrylate of 40 parts by weight,
2,2,3,3,4,4,5,5-octafluoropentylmethacrylate of 13 parts by weight,
1-hydroxycyclohexylphenylketone of 0.2 parts by weight, and
hydroquinone of 0.1 part by weight were heated and mixed at
60.degree. C. to form uncured substances, and thereafter, the four
kinds of original liquids were simultaneously extruded from a
concentric four-layer composite spinning nozzle to form a
concentric strand fiber. During this extrusion, the viscosities of
the first, second, and third layers were substantially the same as
those of the Example 1, and the viscosity of the fourth
layer-forming components was 2.5.times.10.sup.4 poises. The
temperature of the composite nozzle was 60.degree. C.
Thereafter, the same processes as in Example 1 were carried out to
provide a distributed refractive index type optical transmission
plastic article.
When forming the strand fiber, a ratio of discharged quantities of
the first, second, third, and fourth layers was 7:4:1:0.5. The
optical transmission article thus produced had a radius (r.sub.0)
of 0.60 mm, distributed refractive indexes measured by the
Interfaco interference microscope of 1.507 at a central portion and
1.496 at a peripheral portion, and a refractive index distribution
constant (g) of 0.20 mm.sup.-1. A refractive index distribution of
the article substantially approximated the equation (1), in a range
of 0.15r.sub.0 to 0.80r.sub.0 extending from the center toward the
external face of the article. Both end surfaces of the optical
transmission article were polished to a lens length of 18.4 mm, the
MTF thereof was measured with a grid of 4 line-pairs/mm, and it was
found that the MTF was 65% at a conjugate length of 42.4 mm. A
plurality of the optical transmission articles were employed to
form an optical transmission article array having a lens length of
18.4 mm, in a manner similar to the Example 1. An MTF of the array,
measured with a grid of 4 line-pairs/mm, was 58% at a conjugate
length of 42.4 mm. This optical transmission article array, an LED
light source, and a light receiving CCD element were assembled into
an image scanner, which provided a high resolution and was able to
transmit clear images.
EXAMPLE 3
The four kinds of original liquids used in the Example 2 were used
as original liquids for forming first to fourth layers. Poly(methyl
methacrylate)([.rho.]=0.34 measured in MEK at 25.degree. C.) of 40
parts by weight, methylmethacrylate of 18 parts by weight,
2,2,3,3,4,4,6,6-octafluoropentylmethacrylate of 42 parts by weight,
1-hydroxycyclohexylphenylketone of 0.2 parts by weight, and
hydroquinone of 0.1 part by weight were heated and mixed at
60.degree. C. to form a fifth layer, and thereafter, the five kinds
of original liquids were simultaneously extruded from a composite
nozzle to form a concentric strand fiber. During this extrusion,
the viscosities of the first, second, third, and fourth layers were
substantially the same as those of Example 2, and the viscosity of
the fifth layer-forming components was 2.2.times.10.sup.4 poises.
The temperature of the composite nozzle was 60.degree. C.
Thereafter, the same processes as in Example 1 were carried out to
provide a distributed refractive index type optical transmission
plastic article. When forming the strand fiber, a ratio of
discharged quantities of the first, second, third, fourth, and
fifth layers was 7:4:1.1:0.6:0.4. The optical transmission article
thus produced had a radius (r.sub.0) of 0.60 mm, distributed
refractive indexes measured by the Interfaco interference
microscope of 1.507 at a central portion and 1.494 at a peripheral
portion, and a refractive index distribution constant (g) of 0.20
mm.sup.-1. A refractive index distribution of the article
substantially approximated the equation (1), in a range of
0.15r.sub.0 to 0.85r.sub.0 extending from the center toward the
external surface of the article. Both end surfaces of the optical
transmission article were polished to a lens length of 17.8 mm, the
MTF thereof was measured with a grid of 4 line-pairs/mm, and it was
found that the MTF was 72% at a conjugate length of 32.6 mm. A
plurality of the optical transmission articles were formed into an
optical transmission article array having a lens length of 17.8 mm,
in a manner similar to Example 1. An MTF of the array measured with
the grid of 4 line-pairs/mm was 65% at a conjugate length of 32.6
mm. This optical transmission article array, an LED light source,
and a light receiving CCD element were assembled into an image
scanner, which provided a high resolution and was able to transmit
clear images.
COMPARATIVE EXAMPLE 1
The same four kinds of original liquids as those used in the
Example 2 were employed at a ratio of discharged quantities of the
first, second, third, and fourth layers of 1:1:1:1. The other
conditions were the same as those of Example 2 in forming a strand
fiber. The monomers were diffused, and the curing process was
carried out to prepare an optical transmission article having a
radius (r.sub.0) of 0.55 mm, distributed refractive indexes
measured by the Interfaco interference microscope of 1.506 at a
central portion and 1.486 at a peripheral portion, and a refractive
index distribution constant (g) of 0.29 mm.sup.-1. The refractive
index distribution of the article agreed with the equation (1) for
only about 10% of the radial range. Both end surfaces of the
optical transmission article were polished to a lens length of 13.5
mm, and the MTF of the article measured with a grid of 4
line-pairs/mm, was 22% at a conjugate length of 24.7 mm. A
plurality of the optical transmission articles were assembled into
an optical transmission article array having a lens length of 13.5
mm in a similar manner to Example 1. An MTF of the array measured
with the grid of 4 line-pairs/mm was 19% at a conjugate length of
24.7 mm. This optical transmission article array, an LED light
source, and a light receiving CCD element were assembled into an
image scanner, which provided a very poor resolution.
EXAMPLE 4
Poly(methyl methacrylate) ([.rho.]=0.34 measured in MEK at
25.degree. C.) of 51 parts by weight, benzylmethacrylate of 20
parts by weight, methylmethacrylate of 29 parts by weight,
1-hydroxycyclohexylphenylketone of 0.2 parts by weight, and
hydroquinone of 0.1 part by weight were heated and mixed at
60.degree. C. to form an uncured substance as an original liquid
for forming a first layer. The original liquid for forming the
third layer used in the Example 1 was used as an original liquid
for forming a second layer. The original liquid for forming the
fourth layer used in the Example 2 was used as an original liquid
for forming a third layer. These three kinds of original liquids
were used to prepare a distributed refractive index type optical
transmission material in a manner similar to the Example 1. At this
time, the viscosity of the first layer-forming components was
4.5.times.10.sup.4 poises.
When forming a strand fiber, a ratio of discharged quantities of
the first, second, and third layers was 7:3:1. The prepared optical
transmission article had a radius (r.sub.0) of 0.46 mm, distributed
refractive indexes measured by the Interfaco interference
microscope of 1.500 at a central portion and 1.490 at a peripheral
portion, and a refractive index distribution constant (g) of 0.25
mm.sup.-1. A refractive index distribution of the article
substantially approximated the equation (1) in a range of
0.15r.sub.0 to 0.81r.sub.0 extending from the center toward the
external face of the article. Both end surfaces of the optical
transmission article were polished to a lens length of 15.6 mm, the
MTF thereof was measured with a grid of 4 line-pairs/mm, and it was
found that the MTF was 62% at a conjugate length of 29.0 mm. A
plurality of the optical transmission articles were employed to
form an optical transmission article array having a lens length of
15.6 mm in a manner similar to Example 1. An MTF of the array
measured with the grid of 4 line-pairs/mm was 55% at a conjugate
length of 29.0 mm. This optical transmission article array, an LED
light source, and a light receiving CCD element were assembled into
an image scanner, which provided a high resolution and was able to
transmit clear images.
EXAMPLE 5
A polymer [A] (n.sub.0 =1.456, [.rho.]=1.00 measured in MEK at
25.degree. C.) of 50 parts by weight composed of methylmethacrylate
of 50% by weight and 2,2,3,3-tetrafluoropropylmethacrylate of 50%
by weight, methylmethacrylate of 50 parts by weight,
1-hydroxycyclohexylphenylketone of 0.2 part by weight, and
hydroquinone of 0.1 part by weight were heated and mixed at
60.degree. C. to form an uncured substance as an original liquid
for forming a first layer. The above polymer [A] of 48 parts by
weight, 2,2,3,3-tetrafluoropropylmethacrylate of 22 parts by
weight, methylmethacrylate of 30 parts by weight,
1-hydroxycyclohexylphenylketone of 0.2 part by weight, and
hydroquinone of 0.1 part by weight were heated and mixed at
60.degree. C. to form an uncured substance as an original liquid
for forming a second layer. The polymer [A] of 46 parts by weight,
2,2,3,3-tetrafluoropropylmethacrylate of 44 parts by weight,
methylmethacrylate of 10 parts by weight,
1-hydroxycyclohexylphenylketone of 0.2 part by weight, and
hydroquinone of 0.1 part by weight were heated and mixed at
60.degree. C. to form an uncured substance as an original liquid
for forming a third layer. The three kinds of original liquids were
spun to form a composite in a manner similar to Example 1 at the
viscosities of 4.0.times.10.sup.4 poises for the first
layer-forming components, 3.3.times.10.sup.4 poises for the second
layer-forming components, and 3.1.times.10.sup.4 poises for the
third layer-forming components.
When forming the strand fiber, a ratio of discharged quantities of
the first, second, and third layers was 7:4:1. The prepared optical
transmission article had a radius (r.sub.0) of 0.50 mm, distributed
refractive indexes measured by the Interfaco interference
microscope of 1.472 at a central portion and 1.459 at a peripheral
portion, and a refractive index distribution constant (g) of 0.27
mm.sup.-1. A refractive index distribution of the article
substantially approximated the equation (1), in a range of
0.15r.sub.0 to 0.78r.sub.0 extending from the center toward the
external face of the article. Both end surfaces of the optical
transmission article were polished to a lens length of 14.0 mm, the
MTF thereof was measured with a grid of 4 line-pairs/mm, and it was
found that the MTF was 64% at a conjugate length of 29.0 mm. A
plurality of the optical transmission articles were employed to
form an optical transmission article array having a lens length of
14.0 mm in a manner similar to Example 1. An MTF of the array
measured with the grid of 4 line-pairs/mm was 57% at a conjugate
length of 29 mm. This optical transmission article array, an LED
light source, and a light receiving CCD element were assembled into
an image scanner, which provided a high resolution and was able to
transmit clear images.
INDUSTRIAL APPLICABILITY
Compared with an optical transmission article of a prior art of the
same kind, the distributed refractive index type optical
transmission plastic article of the invention substantially
approximates the ideal distribution curve of the equation (1), at
least in a range of 0.25r.sub.0 to 0.75r.sub.0 from the center of
the article, and therefore, without a cutting of the peripheral
portion thereof, the article of the invention provides excellent
lens characteristics. The distribution refractive index type
optical transmission article of the invention, therefore, can be
applied to an image transmitting array of a copying machine
employing a white light source, and to an optical transmission line
such as a near parabolic optical fiber, a rod-like convergent lens,
and an optical sensor.
The optical transmission article of the invention can be
efficiently manufactured by a multilayer extrusion method of
concentrically extruding more than three layers from uncured
substances.
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